docs: def masked(self) -> np.ndarray:
          """Axis expression evaluated, and masked with NaN shared from data channels."""
          arr = self[:]
          arr.shape = self.shape
          arr = wt_kit.share_nans(arr, *self.parent.channels)[0]
          return np.nanmean(
              arr, keepdims=True, axis=tuple(i for i in range(self.ndim) if self.shape[i] == 1)
          )